1. Field of the Invention
The present invention relates to an electrode plate and its manufacturing method, and a gas discharge panel having an electrode plate and its manufacturing method.
2. Related Art
An electrode plate, in which electrodes are formed by laminating transparent electrodes made of indium tin oxide (ITO) or the like and bus lines made of metal (Ag or Cr—Cu—Cr) or the like on a surface of a plate such as a glass plate, is being used in a number of applications such as a front panel having display electrodes in a gas discharge panel.
A gas discharge panel, typified by a plasma display panel (PDP), is a type of flat display panel (FDP) that lends itself to use in a large-screen device. 50-inch class devices have already been commercialized using PDPs.
In a PDP, two thin glass plates (front panel glass and back panel glass) are placed in opposition to each other, with barrier ribs being interposed in between. Phosphor layers are formed in the gaps between neighboring barrier ribs. Discharge gas is filled in the discharge spaces present between the two glass plates, and the two glass plates are sealed together so as to be airtight. A plurality of pairs of display electrodes are disposed on the surface of the front panel glass facing the phosphor layers. By initiating discharge of gas in each of the discharge spaces, ultraviolet light is produced.
FIG. 8A is a perspective view showing an example electrode plate that includes a front panel glass 21 and a pair of display electrodes 22 and 23 disposed on the front panel glass 21. FIG. 8B is a top view of the pair of display electrodes 22 and 23, looking down in a direction z. As illustrated, the display electrodes 22 and 23 are each extending in such a direction (i.e. direction y) as to intersect with barrier ribs 30. These display electrodes 22 and 23 are made up of transparent electrodes 220 and 230 which are strip-shaped ITO films, and bus lines (bus electrodes) 221 and 231 of Ag having high conductivity which are deposited respectively on the transparent electrodes 220 and 230. The areas between neighboring barrier ribs 30 are cell's 340, in which phosphor layers (not illustrated) in each of the three colors red (R), green (G), and blue (B) are formed. In the cells 340, ultraviolet light produced between the display electrodes 22 and 23 collides with and excites the phosphor layers, as a result of which visible light is emitted and put to use in screen display. In ordinary PDPs, a plurality of cells such as the cells 340 are aligned for a plurality of pairs of display electrodes such as the pair of display electrodes 22 and 23, thereby forming a matrix.
Here, the display electrode 22 (23) is formed by applying a paste containing a conductive material, an organic material, and a glass substance to the surface of the front panel glass 21 (the surface of the transparent electrode 220 (230) in the case of the bus line 221 (231)) in a predetermined pattern by screen printing (a thin film or thick film formation method), and then firing the result.
However, when the display electrode 22 (23) is formed on the front panel glass 21 according to this manufacturing method, the display electrode 22 (23) may become misaligned or part of the display electrode 22 (23) (such as the bus line 221 (231)) may peel away from the surface to which it has been adhered. These problems arise due to the following main reasons.
First, the adhesion between the transparent electrode 220 (230) or the bus line 221 (231) and the surface to which it is adhered (i.e. the surface of the front panel glass 21 or the surface of the transparent electrode 220 (230)) depends on an affinity at an interface between the two members. If the affinity is insufficient, the adhesion between them is not strong. Accordingly, when the display electrode 22 (23) suffers vibrations created during the process of firing the bus line material or during transportation in the subsequent process of forming a dielectric layer over the formed display electrode 22 (23), the above problems are likely to occur.
Second, the display electrode 22 (23) is formed by firing a paste including a conductive material, an organic material, and a glass substance, as noted earlier. In this firing process, the organic material is destroyed, which causes the display electrodes 22 (23) to slightly shrink in volume. Since this destruction of the organic material occurs gradually from the surface of the paste, the transparent electrode 220 (230) or the bus line 221 (231) is acted upon by stress that induces warping (deformation stress), and as a result becomes prone to peel away from the surface to which it is adhered. In particular, the outermost end of the bus line 221 (231) in the direction in which it extends (the direction y in FIG. 8) tends to peel away from the surface of the transparent electrode 220 (230). The inventors of this patent application have found that such phenomenon is frequently observed when the bus line 221 (231) contains Ag.
These problems may arise even if a method other than screen printing, such as sputtering, is employed in the formation of the bus line 221 (231). In the sputtering method, due to factors such as the internal atmospheric pressure and the plate temperature (the temperature of the front panel glass 21) during sputtering, stress acts on a film of bus line material which is being developed. The developed film is then etched using photolithography or the like to form the bus line 221 (231). During this etching, the film tends to become misaligned or peel away from the transparent electrode 220 (230), due to the above stress.
Similar problems are seen in electrode plates of other flat panel display (FPD) technologies (e.g. a front panel glass having display electrodes in a liquid crystal display). Immediate solutions to these problems are crucial for the development of efficient FPDs.